A forum attached to a website brings a number of benefits to the site owner. First and for most as the membership of the forum increases it makes the site more "sticky". That simply means that the members of the forum must return again and again to the website in order to gain access to the forum thus generating traffic to the site that can develop additional sales of your goods and services.
The owner of the forum has the ability to send bulk emails to all members thus creating a no cost venue for advertising. As the membership of the forum grows the strength of the advertising impact is proportional.
With forums you can:
Blogs allow a company to control the editorial content of the website. With blogs and forums a company can utilize an informal, conversational style of writing. Both blogs and forums provide opportunities for product feedback.